package edu.thu.thss.yxy.sip.security;

import java.security.*;

import edu.thu.thss.yxy.util.Logger;

/**
 * The class takes standard Http Authentication details and returns a response
 * according to the MD5 algorithm
 * 
 * @author Andy Gao
 * 
 */
public class MessageDigestAlgorithm {
	private static final Logger logger = Logger
			.getLogger(MessageDigestAlgorithm.class);

	/**
	 * Calculates an http authentication response in accordance with rfc2617.
	 * <p>
	 * 
	 * @param algorithm
	 *            a string indicating a pair of algorithms (MD5 (default), or
	 *            MD5-sess) used to produce the digest and a checksum.
	 * @param username_value
	 *            username_value (see rfc2617)
	 * @param realm_value
	 *            A string that has been displayed to the user in order to
	 *            determine the context of the username and password to use.
	 * @param passwd
	 *            the password to encode in the challenge response.
	 * @param nonce_value
	 *            A server-specified data string provided in the challenge.
	 * @param cnonce_value
	 *            an optional client-chosen value whose purpose is to foil
	 *            chosen plaintext attacks.
	 * @param method
	 *            the SIP method of the request being challenged.
	 * @param digest_uri_value
	 *            the value of the "uri" directive on the Authorization header
	 *            in the request.
	 * @param entity_body
	 *            the entity-body
	 * @param qop_value
	 *            Indicates what "quality of protection" the client has applied
	 *            to the message.
	 * @param nc_value
	 *            the hexadecimal count of the number of requests (including the
	 *            current request) that the client has sent with the nonce value
	 *            in this request.
	 * @return a digest response as defined in rfc2617
	 * @throws NullPointerException
	 *             in case of incorrectly null parameters.
	 */
	static String calculateResponse(String algorithm, String username_value,
			String realm_value, String passwd, String nonce_value,
			String nc_value, String cnonce_value, String method,
			String digest_uri_value, String entity_body, String qop_value) {
		logger.debug("trying to authenticate using : " + algorithm + ", "
				+ username_value + ", " + realm_value + ", "
				+ (passwd != null && passwd.trim().length() > 0) + ", "
				+ nonce_value + ", " + nc_value + ", " + cnonce_value + ", "
				+ method + ", " + digest_uri_value + ", " + entity_body + ", "
				+ qop_value);

		if (username_value == null || realm_value == null || passwd == null
				|| method == null || digest_uri_value == null
				|| nonce_value == null)
			throw new NullPointerException(
					"Null parameter to MessageDigestAlgorithm.calculateResponse()");

		// The following follows closely the algorithm for generating a response
		// digest as specified by rfc2617
		String A1 = null;

		if (algorithm == null || algorithm.trim().length() == 0
				|| algorithm.trim().equalsIgnoreCase("MD5")) {
			A1 = username_value + ":" + realm_value + ":" + passwd;
		} else {
			if (cnonce_value == null || cnonce_value.length() == 0)
				throw new NullPointerException(
						"cnonce_value may not be absent for MD5-Sess algorithm.");

			A1 = H(username_value + ":" + realm_value + ":" + passwd) + ":"
					+ nonce_value + ":" + cnonce_value;
		}

		String A2 = null;
		if (qop_value == null || qop_value.trim().length() == 0
				|| qop_value.trim().equalsIgnoreCase("auth")) {
			A2 = method + ":" + digest_uri_value;
		} else {
			if (entity_body == null)
				entity_body = "";
			A2 = method + ":" + digest_uri_value + ":" + H(entity_body);
		}

		String request_digest = null;

		if (cnonce_value != null
				&& qop_value != null
				&& nc_value != null
				&& (qop_value.equalsIgnoreCase("auth") || qop_value
						.equalsIgnoreCase("auth-int")))

		{
			request_digest = KD(H(A1), nonce_value + ":" + nc_value + ":"
					+ cnonce_value + ":" + qop_value + ":" + H(A2));

		} else {
			request_digest = KD(H(A1), nonce_value + ":" + H(A2));
		}

		return request_digest;
	}

	/**
	 * Defined in rfc 2617 as H(data) = MD5(data);
	 * 
	 * @param data
	 *            data
	 * @return MD5(data)
	 */
	private static String H(String data) {
		try {
			MessageDigest digest = MessageDigest.getInstance("MD5");

			return toHexString(digest.digest(data.getBytes()));
		} catch (NoSuchAlgorithmException ex) {
			// shouldn't happen
			logger.error("Failed to instantiate an MD5 algorithm", ex);
			return null;
		}
	}

	/**
	 * Defined in rfc 2617 as KD(secret, data) = H(concat(secret, ":", data))
	 * 
	 * @param data
	 *            data
	 * @param secret
	 *            secret
	 * @return H(concat(secret, ":", data));
	 */
	private static String KD(String secret, String data) {
		return H(secret + ":" + data);
	}

	// the following code was copied from the NIST-SIP instant
	// messenger (its author is Olivier Deruelle). Thanks for making it public!
	/**
	 * to hex converter
	 */
	private static final char[] toHex = { '0', '1', '2', '3', '4', '5', '6',
			'7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

	/**
	 * Converts b[] to hex string.
	 * 
	 * @param b
	 *            the bte array to convert
	 * @return a Hex representation of b.
	 */
	private static String toHexString(byte b[]) {
		int pos = 0;
		char[] c = new char[b.length * 2];
		for (int i = 0; i < b.length; i++) {
			c[pos++] = toHex[(b[i] >> 4) & 0x0F];
			c[pos++] = toHex[b[i] & 0x0f];
		}
		return new String(c);
	}
}
